The present invention relates generally to an indirect-fired climate control apparatus for modifying certain aspects of air flowing through a controlled environment, and more particularly to such an apparatus which employs a rotary energy exchange device with means for bilaterally introducing/extracting energy from the primary and secondary air flows, and wherein means are provided for more efficiently utilizing the energy available in the primary air flow from which energy is introduced to the secondary side.
In the past, rotary energy exchange devices have been employed for use in connection with indirect systems for modifying certain aspects of environmental air, including modification through heating, cooling, humidifying, dehumidifying, and the like. As such, the rotary energy exchange device which rotates through the primary and secondary flows has been normally designated as a "heat wheel". Typically, the rotary energy exchange device utilizes discrete energy exchange means which are located radially outwardly of the axis of rotation of the wheel, and are alternately exposed to primary and secondary air flows wherein energy is introduced into the exchange means on the primary portion of the arcuate travel, and extracted from the exchange means on the secondary portion of travel. In these systems, the primary flow is provided with a means for introducing energy to the system, typically by way of a burner, while the secondary air flow is designed to extract that energy from the exchange means.
In the past, burners have been employed with heat wheels, with the burner output or gases being introduced into the primary air flow. After contacting that portion of the heat wheel within the first or primary air flow, and following extraction of a portion of the energy therefrom, the spent combustion gases are discharged from the system through an exhaust outlet. Inasmuch as there is typically a considerable amount of energy remaining in the combustion air or gases, the present invention provides a system wherein additional energy may be extracted from the combustion air. This is undertaken by creating the primary flow with makeup air or gases from three separate sources, these being fresh outdoor air, gaseous discharge from the combustion burner, and with a third component being recycled from partially spent portion of the combustion air of the second component. Accordingly, the charge of air which includes components from the gaseous output of the burner, together with other components is recycled in order to extract an additional quantity of energy from that portion of the combustion air. The additional utilization of the recycled component reduces the energy input otherwise required from the burner, while maintaining the heat wheel in an appropriate environment for performing its step in the overall operation. By way of further example, the recycled component may be blended with incoming fresh outdoor air, or alternatively, the three components may be blended at a point downstream from the burner output.